| Huozhou(HZ) coal, which was seldom studied before, was investigated in the fluidized-bed reactor to study sulfur removal during pyrolysis in nitrogen atmosphere and nitrogen with different oxygen contents, and the mechanism of sulfur removal was studied by PY-MS.The sulfur removal during pyrolysis in the fluidized-bed reactor It was found by comparing the pyrolysis of HZ coal in N2 and varying content of oxygen that the optimal condition of sulfur removal is in5.5%O2-N2 atmosphere at the temperature of 700℃. Oxygen selectivelybreaks C-S bonds other than C-C bonds under that condition. With increasing oxygen content, more C-C bonds are broken together with C-S bonds, which results in decrease in char yields. The proportion of sulfurdistributed in tar increases with the temperature up to 700℃in the atmosphere with the same oxygen content, and also increases with oxygen content increasing at the same temperature except for 800℃. There is no marked difference between the sulfur removed to tar in 5.5%O2-N2 atmosphere and in- 8.5%O2-N2 atmosphere, which suggests that higher oxygen contents can oxide organic sulfur structure in tar, so more sulfur evolves to pyrolytic gas.The analysis of pyrolytic gases It was found that the evolution profiles of SO2 and H2S are almost the same in inert atmosphere, which indicates that sulfur-containing radicals can equally react with the hydrogen and oxygen in coal. The evolution of COS is mainly related to organic sulfur structure, not the pyrite in coal. In addition, small amounts of CS2 and C4H4S were also measured by PY-MS.In 1%O2-He atmosphere, pyrite and unstable organic sulfurs can decompose at lower temperatures than in inert atmosphere, which indicates that the effects of sulfur removal is better under oxidative atmosphere, and the most important thing is that not only unstable organic sulfur but a part of stable organic sulfur can also be removed atlower temperature (600℃). Under 1%O2-He atmosphere, the evolution ofCOS enhances than in inert atomosphere. Comparison of the evolution of pyrolytic gases of raw, deashed and pyrite-free coals, indicates that oxygen selectively breaks C-S and C-C bonds during pyrolysis. At lower temperatures oxygen breaks C-S bonds at first. With increasing temperature, C-C bonds can also be broken along with C-S bonds. Under 2%O2-He atmosphere, the decomposition temperature of unstable organic sulfur does not decrease, but the evolution of SO2 and COS increases obviously, and the evolution of SO2 can finish at lower temperature than that in 1%O2-He atmosphere.Under oxidative atmospheres, the evolution of sulfur-free pyrolytic gases decreases compared with that under inert atmosphere. But in 2%O2-He atmosphere the evolution of a part of sulfur-free gases is more than that in 1%O2-He atmosphere. This suggests that with higher oxygen content in atmosphere, the more C-C bonds are broken, so char yields decrease quickly, which results in the losing in the significance of sulfur removal.
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